In a process of manufacturing an item such as a semi-conductor device, a liquid crystal panel, and a disk, there is a step for subjecting a substrate of each item to a treatment using plasma. In a system which performs such plasma treatment step, high-frequency power is supplied from the high-frequency power source to change processed gas into plasma, and using this plasma, a surface of the substrate is subjected to a film formation or an etching treatment. In such system in vacuum, a matching circuit is provided between the high-frequency power source and a load, so as to adjust impedance reaching the plasma from the matching circuit and impedance reaching the high-frequency power supply from the matching circuit, thereby exercising control for suppressing a reflected power from the plasma.
In a treatment which employs plasma such as the film formation and etching, an abnormal electrical discharge may take place due to various factors, such as an arrangement of magnet part, a state of cathode surface, a method for manufacturing an insulated part; a quality of target, a manufacturing method, a shape of edge part, erosion, a surface corrosion state, and homogeneities of surface activation, and a temperature control method thereof; and a type of sputter gas, a pressure control thereof, and a way how to flow the gas.
As for the abnormal electrical discharge, initially, a minority arc is generated, and subsequently, energy is concentrated due to a temperature rise at the minority arc part, and then a transition is made to a majority abnormal discharge (a majority arc). When this majority arc is generated, a positive feedback occurs in movement of high-energy electron, a rise of the surface temperature of the target, and an abnormal distribution of gas pressure. Accordingly, evaporation of the target material and rising of local plasma density occur, resulting in triggering of an enormous arc, referred to as “racetrack arc”, for instance. Such minority arc, majority arc, and racetrack arc may physically destroy the target, and in addition to such influence, there is another influence brought about by broken pieces, such as making of pinhole on a memory or on an optical surface in the course of film formation.
When a small oxidized portion is generated on the target due to the destruction, an electron density at the portion becomes higher, and energy accumulated in the plasma itself and additional energy supplied from the high-frequency power source and DC power source are absorbed. Accordingly, impedance around the oxidized portion is radically lowered, and the energy being absorbed is converted into heat. This heat causes evaporation of the material of the target, thereby increasing a partial pressure or making the electron density higher. Therefore, if such major-scale abnormal electrical discharge occurs as described above, it is necessary to release the heat around the target or sample, and apply the power again, after diffusion of gas (see patent document 1).
The electron density within plasma is one of the factors which exert influence on a substrate treatment. The state of plasma is changed according to high-frequency power, pressure within a vacuum chamber, or the like. Therefore, even though the impedance is adjusted by the matching circuit, some plasma conditions may increase a reflected wave, which is reflected by the plasma and returns to the high-frequency power source. There is suggested a technique which monitors the electron density within the plasma, by detecting a reflective coefficient (see patent document 2).
Occurrence of abnormal electrical discharge such as an arc may cause damage to a glass substrate, silicon wafer, or the like. It is suggested that when the arc occurs within a plasma generation chamber in a high-frequency generator, the occurrence of arc is detected by detecting a reflected power, and a control circuit which receives a detection signal lowers or suspends temporarily (for tens of millisecond) the output from the high-frequency generator, thereby achieving arc suppression (see patent document 3).
In order to suppress instantaneous abnormal electrical discharge which occurs on an electrode for film formation, a plasma CVD device is suggested, which is provided with an operational feature, referred to as arc-cut function to suppress the occurrence of abnormal electrical discharge. This arc-cut function detects a sign of occurrence of instantaneous abnormal electrical discharge, according to current or the like within a matching box, and stops application of high-frequency power or reduces the applied power, only for a short period of time (see patent document 4).
The patent document 3 further suggests that the number of arc-cut operation times is counted, so as to record the number of arc-cut operation times during film formation treatment.    [Patent Document 1]    Japanese Patent Application Publication No. 2733454    [Patent Document 2]    Japanese Unexamined Patent Application Publication No. 2000-299198    [Patent Document 3]    Japanese Unexamined Patent Application Publication No. 06-119997    [Patent Document 4]    Japanese Unexamined Patent Application Publication No. 2001-102196